How to get DTS(-HD) thru HDMI on my Pioneer HTP-500 home theather system?

A brief lookup of the Pioneer system does not indicate that it speciffically decodes DTS-HD but DTS systems are backward compatible so It should, at least, decode DTS-ES from the HD bitstream. The HDMI connection is fine. You should set your BluRay player to "Raw" or enencoded bitstream. If set to "audio PCM", it is basically sending 2 channel audio to your reciever. The reciever might synthesize surround sound or play it out of all 5 speakers but it is not true surround...I don't know enough about your BluRay player, but if setting to "raw" doesn't show up at the reciever, you might try to connect audio via optical ot SPDIF cable, but HDMI should work.